It is well-known to mount a damper in the holder to suppress chattering utilizing inertia. Particularly in the case of inner diameter machining boring tools, because the size of the holder is restricted by the bore diameter of the workpiece, its protrusion has to be increased while reducing the diameter of the shank. This increases the possibility of chattering. Thus, many of the conventional vibration suppressing tools are boring tools. The following description is therefore mainly made with reference to boring tools.
For example, in Patent document 1, a method shown in FIG. 5 is disclosed. In this method, a hole 21 is formed in the holder 1 from its rear end, a damper 22 is received in the hole 21 at its front end near the cutting edge, and a core rod 23 is inserted in the hollow portion of the hole. In Patent document 2, a turning tool is disclosed of which the holder is formed with a deep hole in its central portion into which a viscous fluid and a weight are received. In Patent document 3, a cutting tool is disclosed in which a rod spring is inserted in a hole formed in the tool body, a visco-elastic body is disposed between the rod spring and the hole, a cutting head is provided at the front end of the rod spring, and a frictional vibration suppressing material is provided between the cutting head and the tool body.
The cutting tools shown in Patent documents 1 and 2 cancel chattering using the inertia of the damper. The cutting tool disclosed in Patent document 3 reduces vibrations transmitted to the tool body by converting vibration energy to frictional heat.
There are also known a boring bar in which a damper made of a different material from the shank is fitted in a hole formed in the shank using tapered surface to damp vibration utilizing the contact friction between the shank and the damper (see Patent document 4), and tools in which a vibration suppressing member for absorbing vibration energy is mounted in the tool body to damp vibration (Patent publications 5 and 6).
In the vibration suppressing cutting tools of Patent documents 1 to 3, because the damper is inserted in the deep hole formed in the shank, the hole has to be formed by e.g. a gun drill especially if the tool is an inner diameter machining tool, of which the shank is long and small in diameter, so that the machining cost is high. Also, the hole has a large hollow portion through which the damper is inserted. Such a large hollow portion lowers the rigidity of the holder. Further, the structure is complicated, which also pushes up the cost.
Because these holders are complicated in structure, the diameter of the shank is restricted (so that the diameter of the bore that can machined is also restricted in the case of inner diameter machining). This means that in order to sufficiently damp vibration, the cutting conditions are restricted.
The tools disclosed in Patent documents 4 and 5 also have the same problems. Also, in order to absorb vibration energy with the vibration suppressing material, it is necessary that the vibration suppressing material be made of a material having a high vibration suppressing ability, such as an Mn—Cu vibration suppressing alloy. But such alloys are expensive and formability of these alloys is not good, either. Thus, it is difficult to manufacture a tool that is both less costly and of high performance.
For tools using a vibration suppressing material, if the amount of the vibration suppressing material is reduced to reduce the cost, it is difficult to sufficiently damp vibration. If the amount of the vibration suppressing material is increased, the rigidity and strength of the tool tend to be low, which results in increased deflection and reduced durability of the tool.
In the arrangement in which vibration is damped utilizing the contact friction between the shank and the damper, if the friction area is increased in order to increase the vibration suppressing effect, portions that have to be machined increase, thus increasing the cost. If the damper is not in sufficiently close contact with the shank, the rigidity of the tool tends to increase, so that vibration may increase, rather than decrease, during cutting.    Patent document 1: JP patent publication 2003-136301A    Patent document 2: JP patent publication 6-31507A    Patent document 3: JP patent publication 2979823B    Patent document 4: JP patent publication 6-31505A    Patent document 5: JP patent publication 2001-96403A    Patent document 6: JP patent publication 2003-62703A